Uh please help me, I need a step by step answer.

B 1296

Step-by-step explanation:

Area of a rectangle = Length × Width

Area of a triangle = × Base × Height

3 sides are rectangles with the measurements of (9mm by 21mm)

So 3(9 × 21) = 567mm^2

6 sides are rectangles with the measurements of (9mm by 9mm)

So 6(9 × 9) = 486mm^2

1 side is a rectangle with the measurements of (9mm by 15mm)

So (9 × 15) = 135mm^2

2 sides are triangles with unknown, but equal bases.

To calculate the base, you subtract 9 from 21:   21 - 9 = 12mm

Therefore the base = 12mm

The other measurement can be found by looking to the left of the triangle (9mm from the side)

So   2( × 12 × 9) = 108mm^2

Add the sides up:

567 + 486 + 135 + 108 = 1296 mm^2

d i think

step-by-step explanation: